fix: resolve C3 export login flow and add tests

[Armaldio]

Problem

The Construct 3 export login flow broke due to changes on the Construct 3 website. The old approach:

1. Used UI automation to click through login dialog iframes
2. Injected credentials via raw IndexedDB on the account.construct.net origin

Root cause: The editor reads login state from its own origin (editor.construct.net), not account.construct.net. Cross-origin IndexedDB is not shared. The UI selectors also changed on the C3 site.

Fix

Login flow (script.ts):

• Call account.construct.net/login.json API directly (version-agnostic, stable endpoint)
• Wait for localforage to be available in the editor's JS context
• Inject credentials via localforage on the editor's own origin
• Reload to apply login state

Listener improvements:

• All 8 dialog listeners registered immediately after navigation/login (before file chooser), not after
• notNowBtn listener now re-registers itself recursively
• Added registerNewVersionAvailableListener (was missing)
• All catch handlers guard against "Target page, context or browser has been closed"

Tests

Unit tests (export.test.ts - 11 static analysis tests):

• Verify correct login patterns (localforage, API, origin ordering)
• Verify old broken patterns are removed (raw IndexedDB, UI selectors, wrong origin)
• Verify listener ordering, recursion, and browser-closed guards
• 10/11 fail on the old code, 11/11 pass on the fixed code

E2e tests (construct-export.spec.ts):

• Parameterized across 4 Construct 3 versions: stable (latest), stable r495-2, beta, LTS r449-5
• Tests both logged-out and logged-in export for each version
• Requires packaged Electron binary (pnpm package) to run